题目

   A Chinese traffic policeman prevented a terrible accident thanks to his experience. His action helped him win a lot of praise from the world.    Li Weiqi, the traffic policeman on duty on April 21, was working at a big busy crossing in Hangzhou. At some point, he noticed there was something strange about the road, as small cracks showed.    Li didn’t miss the signal of danger. He directed passing cars to get away from the questionable road part. It was not an easy job as the crossing was quite busy. Soon, he brought some road cones(锥形警告路标)from nearby. His partner不定项选择属于狭义相对论基本假设的是：在不同的惯性系中A．真空中光速不变 B．时间间隔具有相对性 C．物体的质量不变D．物体的能量与质量成正比